The present invention concerns the field of prefilled and disposable needleless syringes; such syringes are used for intradermal, subcutaneous and intramuscular injections of liquid active principle intended for therapeutic use in human or veterinary medicine.
A first imperative for prefilled syringes is that of the compatibility in the long term, generally three years, between the liquid active principle and the reservoir which contains it. Another imperative, associated with the prefilling method, is that of having a transparent reservoir in order to be able to carry out the regulatory checks of correct filling of the reservoir before it is fitted in the syringe. These imperatives result in the production of a reservoir which is substantially transparent and made of a material which is compatible with the active principle for the desired length of time: this material is generally glass for pharmaceutical use: glass type I or II.
The initial phase of the injection is critical for the penetration, into the skin, of the jet or jets of liquid, depending on whether the syringe has one or more injection conduits. The latter configuration being favorable for reducing pain. The final bioavailability depends on the correct implementation of this initial phase, it assumes a rapid acceleration of the liquid in the injection conduits without the multiple jolts of the jets when there is too great a pressure surge to achieve this rapid acceleration.
The prior art does not disclose syringes, with several injection conduits, meeting all of these requirements.
The patent FR 2 775 603 describes a needleless syringe with a prefilled ampule closed at its upstream end by a displaceable obturator and at its downstream end by a multi-hole injector having a central filling orifice closed by a stopper after the ampule has been filed.
The U.S. Pat. No. 4,668,223 describes a syringe with a prefilled ampule which is closed at each of its ends by a displaceable obturator, the upstream end of the ampule receives a guide piece for a plunger rod and the downstream end receives a part forming a receptacle in which the downstream obturator is to be housed.
The U.S. Pat. No. 4,941,880 describes a syringe which is very complex from several points of view. First, it is a syringe with a pneumatic drive, intended to be used several times by changing the ampule containing the active principle. This ampule containing the active principle comprises two juxtaposed parts. An upstream part, for long-term storage of the active principle: this is a glass tube closed at its two ends by obturators and placed in a polycarbonate tube; this arrangement ensures the compatibility and allows the filling to be checked. Before use, the operator transfers the active principle into the downstream part of the ampule, which has the role of intermediate reservoir, by pushing a plunger which displaces the liquid and the downstream obturator; this downstream part of the reservoir is made of polycarbonate and has a thick wall, it will withstand the operating pressure generated by the drive device. The operator places the ampule, thus prepared for injection, into the injection mechanism; upstream of an injection device comprising a single injection conduit which will be supplied via a bypass placed at the downstream end of the intermediate injection reservoir. This arrangement solves the problems of resistance of the reservoir and to a certain extent can reduce the initial jolts of the injection, but with considerable pressure losses in a tortuous injection system for supplying a single injection conduit. The complexity of the device both in terms of its production and its use is self-evident.